RLC Circuit Bandwidth

Formula

Description

The bandwidth of a resonant RLC circuit is the range of frequencies over which the response is within 3 dB of its peak value. Higher Q means narrower bandwidth and sharper selectivity, while lower Q gives a broader, flatter response. This relationship is fundamental to tuned circuit design in receivers, transmitters, and filters. The -3 dB bandwidth is symmetric on a logarithmic frequency scale around the center frequency. For a series RLC circuit, BW = R/(2πL), showing that lower resistance gives narrower bandwidth.

Variables

• BW — -3 dB bandwidth (Hz)
• f0 — Resonant (center) frequency (Hz)
• Q — Quality factor (dimensionless)

Practical Notes

In filter design, the required Q determines component sensitivity and implementation difficulty. Q values above 10-20 require tight component tolerances. Active filters can synthesize high Q with resistors and capacitors. For very high Q requirements (>1000), crystal or ceramic resonators are used instead of LC circuits.